require 'external/io'
require 'external/chunkable'
require 'external/enumerable'
require 'tempfile'

module External
  
  #--
  # Base provides the basic array functionality shared by ExtArr and Index,
  # essentially wrapping the IO functions required to access and utilized external
  # array data with the standard array functions.  Bases can be opened with 
  # in any of the IO modes; the capabilities of Base will be reduced accordingly
  # (ie read-only Bases cannot write values using []=, for instance).  
  #
  # It is VERY IMPORTANT to realize that the underlying IO will be opened using the
  # given mode.  The 'w' mode will overwrite all existing data; 'r+' is a safer mode
  # for full read-write functionality.  Note that since Base actively scans over
  # the IO, append modes essentially behaves like write, but does not overwrite existing
  # data.
  #
  # To work properly, Base must be subclassed with methods:
  # * length
  # * io_fetch
  #++
  #
  #
  class Base
    class << self
      def open(fd=nil, mode="r", options={})
        fd = File.open(fd, mode) unless fd == nil
        ab = self.new(fd, options)
        
        if block_given?
          begin
            yield(ab)
          ensure
            ab.close
          end
        else
          ab
        end
      end
    end
    
    include External::Enumerable  
    include External::Chunkable
 
    attr_reader :io
    
    # Initializes a new Base given the file descriptor, mode and options.
    # (see open_io for details on what io is opened for a given file descriptor)
    #
    # If mode contains an 's', then the Base will be initialized in strio 
    # mode where the underlying IO will be a StringIO.  In this case the fd 
    # will be used as the string to initialize the StringIO.
    #
    # Standard options for Base include:
    # nil_value:: the value written to file for nils, and converted to nil on read
    #             (default ' ')
    # max_gap:: the maximum gap size used by Offset (default 10000)
    # max_chunk_size:: the chunk size used by Offset (default 1M)
    def initialize(io=nil)
      self.io = (io.nil? ? Tempfile.new("array_base") : io)
    end
 
    # True if io is closed.
    def closed?
      io.closed?
    end
  
    # Closes io.
    def close
      io.close unless io.closed?
    end
    
    protected
    
    # Sets io and extends the input io with External::Position.
    def io=(io)
      io.extend External::IO unless io.kind_of?(External::IO)
      @io = io
    end

  end
end